The present invention is directed to improved methods and apparatus for preparing the ends of large diameter metal pipe employed in cross-country pipelines for welding.
Pipe employed in cross-country pipelines, such as the Alaska pipeline, is made up of individual pipe sections which are welded to each other end-to-end at the site of installation. The individual pipe sections are constructed of metal and are relatively large-sized; the typical dimensions of an individual pipe section being a length of 40 feet, a diameter of 30, 40 or more inches, and a wall thickness of one-half of an inch to three-quarters of an inch. Because pipelines of the type here under consideration frequently extend for hundreds of miles and pass through remote sections of country, the individual pipe sections must be transported from their place of manufacture over long distances to their point of installation and frequently must be stored or stock-piled at locations in the field. In the course of this transporting, handling and storage, the pipe sections are subjected to rough handling, prolonged exposure to weather and other adverse conditions.
The achievement of a good weld between abutting ends of pipe sections requires that the end of the pipe be clean, free of rust, nicks and dents, and that the end edge be accurately beveled to receive the weldment. It is thus known in the art to utilize tooling operable in the field to machine the pipe ends just prior to welding so that the weldment is applied to a clean, freshly machined surface.
However, presently employed pipe end machining techniques typically do not take into account any out-of-roundness of the pipe end, slight variations in diameter which may exist between individual pipe sections and slight variances of the plane of the pipe end from true perpendicularity to the pipe axis. These last two problems normally arise from the manufacturing process where precise dimensioning of the final product must be traded off against production cost. Out-of-roundness is more likely to be generated in the handling of the pipe after it has been manufactured and can result from the commonly employed practice of storing the pipe sections in multi-layer stacks. Where the pipe is of a diameter of 40 inches, a slight degree of out-of-roundness, for example, may produce a degree of mis-alignment over at least a portion of the circumference of two abutted pipe sections sufficient to prevent the formation of a satisfactory welded joint between the two sections.
The present invention is especially directed to a method and apparatus by means of which pipe section ends may be prepared for welding in a manner which forms a pipe end truly circular to a precisely determined diameter so that adjacent ends of adjacent pipe sections may be precisely and truly aligned with each other throughout their entire circumference for the welding operation.